Hi guys!! So we got till next Friday, 26 July, until our rolling frame is due!!

So far, we may be behind time as we wanted to send our parts for waterjetting today, but weren’t able to make it by the 4pm deadline..

In any case, we will continue to refine and CAD out remaining parts such as the seat, the brake and the rear wheel assembly. Then, we plan to waterjet everything next Tuesday, so that we can assemble on Friday!

On another random topic, in order to improve our steering system, we approximated for Ackerman steering geometry. This did not need to involve any crunching of numbers, but we simply adjusted the dimensions of our steering parts, by checking our angles on Solidworks and using general rules-of-thumb. Once accounted for, the inner tire will turn a greater angle than the outer tire, which minimizes the sideways slip of tires when our vehicle makes a turn.

A general rule of thumb is that the lines from the steering kingpins to the steering pivot points on each side, when projected, will intersect at the centre of the rear axle. Something that we achieved with our steering, give and take one degree.

Another thing we could do is to draw concentric circles which imitate the path of our vehicle as it turns. We then check that the inner and outer wheels are turning at the appropriate angle; tangent to its corresponding circular path!

Enough with the steering. Next up we have our seat. We are planning to make one out of wood, and it will be adjustable! More updates soon.. Stay tuned! =)

CADing our frame in Solidworks helped us to better visualize our vehicle, which resulted in us making some changes to the frame and connectors. It helped us to improve upon the structural integrity of the frame, and create connectors that optimize the amount of aluminium plate given to us.

CAD of the steering system

We also split the CAD work among the three of us, as the Solidworks workload was quite heavy, and this way we could all gain some experience in Solidworks as well. We CADed the steering system separately, before assembling this together with the frame.

Our final CAD of the frame and steering system combined

CADing was a good way for us to confirm the dimensions of our frame and other parts, knowing that they will be properly aligned. CADing was also essential in helping us know what parts to order. We ordered more specialised parts such as shoulder screws for our front wheel axles.

Prototyping

All’s good at IDC

The laser-cut connectors and rail

We then put the parts together to form…

A laser cut prototype of our frame – we even laser cut the extruded rails

Guan Yang and Zijian evaluating our frame prototype

A prototype of the seat that we will be mounting onto our vehicle!

Budgeting: What’s there left to purchase?

We now have a total of around $65 left to purchase remaining components for the brake and throttle system, belt and sprocket, seat and electrical system. $65 is not alot, thus we will have to carefully plan for the remainder of our budget! Hopefully it will be enough, otherwise we may have to beg, borrow and steal.

After deciding on a design concept for our electric vehicle, our team went on to planning and ordering parts – to bring our concept into reality! In order to decide on the major components of the powertrain (motor, controller, wheels), we did some initial calculations to find out the power that we needed to supply to our vehicle in order to achieve the desired top speed of approximately 10m/s. However, due to insufficient research and haste, we ordered the ‘wrong’ motor and controller as we did not look out for the right things in the specifications.

Motor: We made an order for the Turnigy D3548/4 1100Kv Brushless Outrunner Motor. However this turned out to be a wrong choice. We learned that in choosing motors, we should be looking out for the following two specs – rpm constant (kv) and internal resistance. For this order, we only looked at the “max power”. Thus we will have to order another motor with a much lower rpm constant below 200Kv.
For our 1100Kv motor, it will not produce enough torque to propel our vehicle forward with a high-enough acceleration. It will only be enough for this:

Controller: Cost $150 – By far our most expensive purchase thus far: KBS24121L,50A,12-24V, Mini Brushless DC Controller. When looking for controllers, we should look out for its “operating voltage” and the “motor current limit, 10 seconds boost” and match it up to our motor. The controller that we have already ordered should be able to work, but we will have to redo some calculations and revise our budget to see if we can purchase a more optimal controller.

Rear wheel: We ordered an 8″ wheel that comes with a band brake assembly, and with belt sprocket.

Front wheels: We decided to order another of the 8″ pneumatic wheel that was given free.

Summary of calculations: We made calculations to find the max velocity and the acceleration, and did up a spreadsheet. These were more important in helping us choose our core components as compared to simply basing our calculations on power transmission.

Second week into building our EV, and we realise that we should have been more careful in ordering our parts. However, all is not lost. Doing more research and asking our instructors more questions beforehand would have probably prevented us from making costly mistakes. For the coming week, we will continue to refine our calculations, and continue to work on the CAD drawing of our vehicle. We intend to submit another BOM this Friday, and we may then begin to build our vehicle next week!

Each of us came up with a concept of how the electric vehicle will look like and they are as follow:

Anissa:

Guan Yang:

Zi Jian:

Through the sharing and evaluating of various ideas from everyone, we came up with this initial design of our team’s electric vehicle!

So why this design? Some of the questions we asked ourselves are:

Should the vehicle be 3-wheeler or a 4-wheeler?

What should the seating position be like?

How is the steering system going to be like?

Should the vehicle be front-wheel driven or back-wheel driven?

We decided on a 3-wheeler due to reasons such as higher maneuverability and lesser stresses on the structure of the vehicle when turning. When a 4-wheeler is doing a turn, one of the fixed wheel at the back will experience much more friction as it is fixed and has a larger turning radius. A 3-wheeler this will help to reduce this problem with one one fixed wheel at the back, not two. This also helps to save cost as we need only to install one motor to the single wheel without the need for a differential gear. Lesser parts translate to lighter weight and a higher efficiency for the vehicle!

For the seating position, we decided that the position of a go-kart-er will be the most intuitive as it is most comfortable to drive the vehicle this way. The same concept applies for the steering system which we will adopt a steering wheel with acceleration and brake pedals.

We decided on a rear-wheel drive with the primary reason being that it is mechanically complex to have a motor at the front with the steering wheels. Another reason is that as the driving force will be generated from the back, it provides a better traction as well as a more comfortable ride when compared to a front-wheel drive in which the driving force is generated at the front and the rest of the vehicle starts to move backwards to conserve momentum (Newton’s 3rd Law).

So far this is only the skeleton of the vehicle and we are looking into a more unique design for our electric vehicle. Stay tuned! (: